Third generation partnership project (3GPP) and Long Term Evolution (LTE) mobile telecommunication systems provide high data rate, lower latency and improved system performances. With the rapid development of “Internet of Things” (IOT) and other new user equipment (UE), the demand for supporting machine communications increases exponentially. To meet the demand of this exponential increase in communications, additional spectrum (i.e. radio frequency spectrum) is needed. The amount of licensed spectrum is limited. Therefore, communications providers need to look to unlicensed spectrum to meet the exponential increase in communication demand.
One suggested solution is to use a combination of licensed spectrum and unlicensed spectrum. This solution is referred to as “Licensed Assisted Access” or “LAA”. In such a solution, an established communication protocol such as Long Term Evolution (LTE) can be used over the licensed spectrum to provide a first communication link, and LTE can be used over the unlicensed spectrum to provide a second communication link.
In LTE Release 13, LAA has been approved to enable LTE usage over unlicensed spectrum in 5 GHz for small cells. To facilitate efficient and fair spectrum sharing, a dynamic spectrum sharing mechanism called listen-before-talk (LBT) may need to be supported based on regulation rules in each country.
Due to the support of LBT, any physical signal or channel transmission has to be based on the channel contention results of LBT. As a result, the existing scheme of continual or periodic reference signal transmission (e.g., CRS, CSI-RS, and DRS) for UE RRM/CSI measurements is no longer feasible. For example, a discovery reference signal (DRS) transmission with a periodicity of 80 ms may suffer from long interruption (e.g., 160 ms) due to a failure of channel contention and thus result in insufficient information for radio resource measurement and scheduling.